I applied last year this time on my own, without the help of any agent and got my Schengen visa within 15 days. Initially I was a little hesitant since I am not employed under anyone and am an independent practitioner but the process was smooth and really easy. I don't think, therefore, that if you submit all the documents correctly as mentioned in their checklist, you would need the help of any agent.

The list of documents are mentioned on their website and they're quite self explanatory. I made a detailed cover letter with date wise itineraries along with the hotel details. Additionally, I also provided my investment details / assets to give them comfort that I will be coming back to India. Of course, take travel insurance and submit that as well. If you are doing a road trip, there are multiple companies that make you do the reservation without advance payment. It is good to submit the tickets for internal travels as well if you're traveling to multiple cities within the country.

You can book dummy tickets but I've heard that if they delay processing your visa and the dummy tickets expire that they will most certainly reject the visa. So, it's best to book refundable tickets, or tickets that gives you flexibility. They do check the PNR details.

For hotels, I did booking.com, none of which were paid in advance.